title: Diagnostic assays for anti-PM/Scl IgG antibodies: heterogeneity in antibody response or lack of standardization?
abstract: BACKGROUND
  The aim of this study was to compare the correlation between new diagnostic methodologies for detecting anti-polymyositis/scleroderma (anti-PM/Scl) IgG antibodies associated with myositis and/or systemic scleroderma assays with existing platforms.
  
  
  METHODS
  Sera from 164 samples previously tested for anti-PM/Scl IgG antibody by immunodiffusion, ID; 171 sera screened for anti-PM/Scl IgG by immunoprecipitation, IP; an additional group of 215 sera tested by ID and 46 healthy blood donor sera were retrospectively evaluated. Anti-PM/Scl IgG antibodies were measured using three PM/Scl-100 specific enzyme immunoassays (EIAs), PM1-alpha (PM1-α) EIA and a line immunoblot assay (LIA) for anti-PM/Scl-75 and -100 IgG antibodies. Selected samples were tested for the presence of antinuclear antibody (ANA) by indirect fluorescent antibody (IFA) assay.
  
  
  RESULTS
  The overall agreement between ID and all anti-PM/Scl IgG EIAs as determined by Crohnbach's alpha was unacceptable (α<0.50). The concordance between the IP and either LIA or PM1-α EIA was greater than 90% however, the best agreement was seen between the IP and LIA PM/Scl-100 assays (98.3%). Compared to the LIA PM/Scl-75 and PM1-α tests, the LIA PM/Scl-100 IgG assay showed the best specificity in the healthy control group.
  
  
  CONCLUSIONS
  Our results demonstrate considerable differences between assays for detecting anti-PM/Scl IgG antibodies which cannot be attributable to heterogeneity in antibody response alone. Further characterization and standardization of these assays are needed.
authors.affiliation: Associated Regional and University Pathologists (ARUP) Institute for Clinical and Experimental Pathology, University of Utah School of Medicine, Salt Lake City, UT 84108-1221, United States.
authors.forename: Troy D
authors.initials: TD
authors.lastname: Jaskowski
authors.forename: Andrew
authors.initials: A
authors.lastname: Wilson
authors.forename: Harry R
authors.initials: HR
authors.lastname: Hill
authors.forename: Anne E
authors.initials: AE
authors.lastname: Tebo
mesh_terms: D000328:Adult; D001324:Autoantigens / Q000276:immunology*; D001774:Blood Chemical Analysis / Q000379:methods* / Q000592:standards*; D000939:Epitopes / Q000276:immunology; D005095:Exoribonucleases; D063326:Exosome Multienzyme Ribonuclease Complex; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood* / Q000276:immunology*; D007158:Immunologic Techniques / Q000379:methods* / Q000592:standards*; D012015:Reference Standards; D015203:Reproducibility of Results
chemical_list: D001324:Autoantigens; D000939:Epitopes; D007074:Immunoglobulin G; D005095:Exoribonucleases; D063326:Exosome Multienzyme Ribonuclease Complex; C077044:EXOSC10 protein, human